Production of magnesium hydroxide



United States Patent O 3,366,451 PRODUC'HN F MAGNESIUM HYDRGXIDE George W. Waidron, Jr., Bay City, and Harry W. Krimbil, Midland, Mich., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Continuation-impart of application Ser. No. 412,166, Nov. 18, 1964. This application Jan. 4, 1967, Ser. No. 613,768

2 Claims. (Ci. 23-201) ABSTRACT F THE DSCLOSURE This specification discloses an improved process for making a magnesium hydroxide product, characterized by a high surface area and small particle size from brines containing, for example, MgCl2 and lime-containing -materials such as dolomite. The process constitutes an improvement to U.S. Patent 3,080,215 and essentially cornprises adding to calcined dolomite (dolime) in a slaking apparatus from about 1.5 to about 80 weight percent, normally to 80 percent, and preferably from about l5 to about 50 weight percent of a magnesium halide-containing brine, along with an aqueous calcium chloride slaking mixture, at a temperature in the slaker of from about 40 to about 90 C., the proportion of brine added to the slaker ybeing directly related to the specific gravity of the slaking liquid within a range of from about 1.07 to about 1.3. The residence time in the slaker is from about 4 minutes to about 3 hours. The resulting dolime slurry is then added to a reaction vessel such as a precipitator along with the remainder of the fresh MgCl2-containing brine solution, whereby the balance of magnesium values are precipitated as Mg(OH)2 employingT a slight stoichiometric excess of Ca(OH)2 precipitant.

CROSS REFERENCE TO RELATED CASES This application is a continuation-in-part of copending application Ser. No. 412,166, tiled Nov. 18, 1964, now abandoned.

BACKGROUND OF THE INVENTION A process for making a magnesium hydroxide product employing dolomite and a MgCl2-containing brine to produce a dense magnesium hydroxide lter cake, containing at least 45 percent Mg(OH)2 and which is low in impurities, is disclosed in U.S. Patent No. 3,080,215, entitled Production of Mg(OH)2 by G. W. Waldron and J. N. Periard. This patented process produces magnesium hydroxide which is suitable for use in making most periclase-type (a sintered form of MgO) refractory products. However, it was discovered that this magnesium hydroxide was not completely suitable in all cases for use in making a high purity, high density, low porosity periclase product. The magnesium hydroxide made from said patented process has an average particle size ranging from about 5.6 to about 10 microns and a surface area ranging from about 6 to about 9 square meters per gram. After pelleting and tiring the magnesium hydroxide product to about 1700 C., the resulting periclase may have a density ranging approximately from about 2.9 to about 3.0 grams per cubic centimeter (gm./cc.). During the periclase manufacturing process, the Mg(OH)2 first is heated to a firing temperature of about 350 C. where it decomposes to MgO. Conventionally, to increase the density of the periclas, it has -been the practice to add sintering agents, such as silica, during the sintering process at the same tiring temperature. However, the use of additives is limited in some cases, since it places a lower maximum use temperature on the refractory due to the formation of flux-like compounds which have relatively low melting points in the periclas.

3,366,451 Patented Jan. 30, 1968 ICC It is a principal object of the instant invention to provide an improvement in the aforementioned patented process which results in the formation of a magnesium hydroxide product which has a particle size within the range of from about 3 to about 5.5 microns and a surface area within the range of from about 10 to about 20 square meters per gram.

It is an additional object of the instant process to provide a magnesium hydroxide product which is suitable for use in the production of high purity, high density, low porosity periclase requiring a substantially lesser amount of sintering agents for density improvement in the periclase product than has been used in the past.

Other uses, object and advantages of the instant invention will be apparent from reading the detailed description thereof in conjunction with the accompanying ligure. The appended figure is a block diagram of one embodiment of the instant improved method.

In general, the instant invention provides an improvement in the method set out in U.S. Patent No. 3,080,215 for the manufacture of a magnesium hydroxide product.

The method set out in U.S. iatent No. 3,080,215 comprises calcining dolomite at a maximum temperature of about 1450 C. to form the corresponding oxides (hereinafter referred to as dolime); slaking the oxides with a slaking liquid comprising an aqueous calcium chloride solution substantially free of magnesium ions and having a specific gravity of at least about 1.07 and preferably not over 1.30 (as measured at about 25 C.) to produce a slaked dolomitic lime slurry containing Ca(OH)2, MgO and Mg(OH)2 hereinafter referred to as a dolime slurry; intermixing the dolime slurry with an aqueous brine solution containing at least about 2 percent by weight MgCl2 for a mixing period of at least about three hours for brines having a low MgCl2 concentration (that is up to about 3.5 Weight percent MgCl2) at a temperature within the range of from about 40 to about 80 C. or for brines more concentrated in MgCl2 for at least about two hours at the indicated temperature, thereby producing a readily filterable magnesium hydroxide suspended in a CaClz-containing brine; separating the thus suspended magnesium hydroxide from the mother liquor, as by ltration; and, Water-washing the resulting magnesium hy droxide filter cake (sometimes called magnesium hydrate). The amount of the dolime slurry to be used must be suicient to provide more than one mole of Ca( OH)2 per mole of MgCl2 present in the aqueous brine reactant.

The present improvement in the hereinbefore described patented process comprises adding to the slaking7 dolime (in a slaking apparatus) from about 1.5 to about Weight percent, preferably from about 10 to about 80 percent, and more preferably from about 15 to about 50 weight percent of the MgCl2-containing brine (based on required for preparation of Mg(OH)2 as set forth hereinbefore) along with the aqueous calcium chloride slaking mixture. The temperature in the slaker is generally within a range of from about 40 C. to about 90 C. The slaking process is continued for a period of from about 4 minutes up to about 3 hours, and preferably from about 6 to about 30 minutes. The amount of the MgCl2-containing brine to be added to the slaker is directly related to the concentration of the aqueous CaCl2 solution being usedV for slaking. Generally, the aqueous CaCl2 slaking solution used in the aforesaid patented process will have a specific gravity of at least from about 1.07 to about 1.3 (measured at 25 C.). For purposes of the present novel improvement, the specific gravity of the aqueous phase or ltrate of the slaking mixture in the slaker will be considered essentially the same as that of the aqueous CaCl2 slaking solution being introduced thereinto. When the slaking iiuid has a high specific gravity, such as, e.g., about 1.20', as in slaking pulverized dolime, from about to about 80 percent, and preferably from about to about 50 percent of the requisite amount of the magnesium chloridecontaining brine is added to the slaker. At lo-w specific gravities of from about 1.07 to about 1.15, such as when slaking unpulverized dolime, the aqueous MgCl2 brine addition is particularly effective in a range of from about 1.5 to a-bout 10 percent, and especially from 2 to 5 percent.

The resulting dolime slurry is then added to a precipitator vessel along with the remainder of fresh MgCl2-containing brine solution. During the precipitation or reaction period of the final mixture, the temperature in said precipitator vessel is maintained at a temperature within the range of from about 40 C. to about 80 C. for a period of for at least about 3 hours for brines containing less than 3.5 weight percent MgCl2 and at least about 2 hours for brines containing more than 3.5 weight percent MgCl2.

Additions of a magnesium halide brine to the slaking apparatus together with aqueous slaking liquids of particular specic gravities when made in accordance with the present invention provides a highly desirable magnesium hydroxide product having suicient ltering characteristics, and a significantly reduced particle size from that conventionally obtained as well as a significantly increased surface area. In general, the `Mg(OH) prod-uct derived from the improved method herein may be characterized by a particle size below about 5.0 to 6.0 microns and a surface area in square meters per gram exceeding about 9 to 10. When the present novel process is carried without observing the brine addition limitations and slaking liquid specific gravities corresponding thereto, lterability, particle size and surface area of the Mg(OH)2 product are detrimentally affected. For example, brine additions of, e.g., from 10 to 80 percent as aforesaid in combination with slaking liquid specific gravities les than, eg., about 1.15, produces a difficult filtering Mg(OH)2, While low additions of brine, e.g., below about 10 percent, in combination with high specific gravity slaking liquids detrimentally affects the improvement otherwise obtained in particle size and surface area.

In an alternative embodiment of the instant improvement in the process disclosed in U.S. Patent No. 3,080,- 215, the dolime slurry prepared from dolime and an aqueous calcium chloride slaking liquid after leaving the slaker is mixed at approximate specific gravity levels, in a mixing vessel, with from about 1.5 to about 80 percent, and preferably from about 15 to about 50 percent, of the requisite amount of the magnesium containing brine while maintaining a temperature in the mixing vessel wit-hin the range of from about 40 to about 90 C. for a period within the range of from about 4 minutes to about 3 hours. The mixture of brine and dolime slurry is then added to a reaction vessel (referred to herein as a precipitator) along with the remainder of fresh MgCl2-containing brine solution and maintained therein for a predetermined period of time. During the reaction period, the temperature in said reaction vessel is maintained at a temperature within the range of from about 40 to about 80 C. for a period of for at least about 3 hours for brines containing less than 3.5 weight percent MgCl2 and at least about two hours for brines containing more than 3.5 weight percent MgCl2. A slight excess of Ca(OH)2 precipitant is maintained in the precipitator over the stoichiometric amount needed to precipitate the magnesium values.

The magnesium hydroxide product resulting from the improved method of the instant invention normally has an average particle size within the range of, e.g., from about 3 to about 5.5 microns and a desirably high surface area within the range of, e.g., from about 10 to about square meters per gram. The periclase product resulting from the use of the magnesium hydroxide product of the instant improved process can have a density without additives within the range, eg., of from about 3.05 to about 3.35 grams per cubic centimeter.

One illustrative embodiment of the present process is shown in the attached drawing. The figure also depicts a pulverizer which is used when higher specific gravity calcium chloride brine is employed, and a recycle line from the precipitator to the slaker, which is used when the precipitator slurry is employed as the slaking liquid. It is to be understood that the depicted embodiment is illustrative of a mode of practicing the invention and is not to be construed as limiting the invention thereto.

The following examples serve to further illustrate the instant invention but are not to ybe construed tas if limiting it thereto.

Example I Runs I and II as described hereinafter are illustrative of the practice of the invention. Additionally, a control or comparative r-un A made in accordance with the process of U.S. Patent No. 3,080,215, without the present improvement, is included for purposes of comparison.

A typical analysis of the dolomite employed in the runs, when ignited to oxides (dolime), had the following percentage composition: about 57.5 percent CaO, about 40.0 percent MgO and about 2.5 percent inerts.

An analysis by weight of a typical brine employed in the runs showed the following salts dissolved therein: about 18.35 percent CaCl2, 3.3 percent MgCl2, about 5.3 percent NaCl, about 1.5 percent KCl, and lesser amounts of other salts including those of strontium, lithium, boron and iron. lts specific gravity was 1.26.

Run Pulverized calcined dolomite and an aqueous CaCl2 slaking liquid plus magnesium chloride brine were continuously fed into an agitated slaking vessel. Feed rates were maintained to provide the quantities of dolime (in pounds per hour), slaking liquid (in gallons per hour) (ie, aqueous calcium chloride and MgCl2 brine) and the inventory times in minutes as shown in the table set out hereinafter. The resulting slaked dolime slurry Was led from the slaker to a precipitator (i.e., reaction vessel). Concurrently with introduction of the dolime slurry into the precipitator, the remainder (in gallons per hour) of the magnesium chloride brine was admitted at a controlled rate to the precipitator. The rate of addition of the brine was controlled to maintain an excess of Ca(OH)2 in the precipitator over the stoichiometric quantity required to react With the MgCl2 in the brine. Precipitated magnesium hydroxide in suspension was formed in the precipitator leaving a substantially magnesium-free mother liquor.

The magnesium hydroxide precipitate was recovered as a cake by periodically passing the slurry into a Bchner funnel subjected to a reduced absolute pressure of about 6 inches of Hg. The magnesium hydroxide cake was water- Washed on the funnel to provide a cake free of mother liquor.

Run Il.-A second study was carried out in accordance with said procedure and using the same reactants and concentrations as set forth in run I except that the amount of MgCl2 brine introduced into the slaker and the precipitator were varied as shown in the table.

Comparazve run (not in accordance with the present invention).-In comparative run A, brine equal to the total requisite amount was added directly t0 the precipitator in accordance with the teaching of U.S. Patent No. 3,080,215 instead or" adding part of the brine to the slaker and part to the precipitator, as in runs I and II.

The slaking and precipitating conditions and the more important characteristics of the precipitated products produced as shown in the table.

An examination of the results of the comparative run A and runs I and II of Example I of the table illustrates the superiority of the instant improved process over the process employed heretofore for making Mg(OH)2 product suitable for use in the manufacture of high density, low porosity periclase. The average particle size of the Mg(OH)2 product produced by the improved process was about 50 percent smaller than the particle size of Mg(OH)2 produced by the patented process. The surface area of the product of the improved process was about 100 percent greater than that produced in the pat- 6 It can be seen from the data in the table for Example IH, run IV, that adding only 5.1 percent of the requisite MgCl2 brine in accordance with the present invention produces a very significant decrease in the average Mg(OH)2 ented process. Further, the resulting periclase made from 5 particle size, and a very signicant increase in Mg( OH )2 the small particle size, high surface area Mg(OH)2 product surface areas. Acceptable periclase densities would be obof the instant process was about 5 percent more dense tained from this Mg(GH)2 product comparable to denthan the periclase manufactured from the Mg(OH)2 prodsities obtained in Example I. uct produced by the conventional process. E l 1V x e Example Il 10 amp The procedure of Example I Was essentially repeated In this example, similar raw materials and the condias run III using equivalent raw materials and similar contions 0f Example `III Were employed. Unground dolime, ditions, except that larger sized equipment and correrecycled precipitator slurry, and Water. as the slaking spondingly higher feed rates were employed, and a 10 per- 15 liquid Were fed continuously to the rotating slaker along cent (by Weight) brine addition to the slaker. The results with 2 percent (run V) and 3.8 percent (run'VI) of the are consistent with Example I and show that when l0 perrequisite MgCl2 brine. The remainder of brine in each cent of the requisite MgCl2 brine was added to the docase was added to the precipitator. The particular slaklime slaker, there was an increase in product surface area ing and precipitation conditions are shown in the ta-ble and a decrease in the average particle size. Acceptable along With the surface area and average Mg(OH)2 parpericlase densities would be obtained from the Mg(OH)2 ticle size data. Similarly, as in Example III, precipitator product comparable to those of Example I. Comparative slurry and Water were added to the slaker to provide a run B carried out in accordance with U.S. Patent 3,080,215 specic gravity of dol-imc slurry filtrate of about 1.085, at is provided for purposes of comparison to illustrate the which essentially all the slaking was accomplished. For improvement of the present invention. purposes of comparison, comparative run D is provided Example H1 as carried out using the method of U.S. Patent 3,080,215. In comparing run D with `runs V and VI, it can be seen Th1S eXamPle 1111189" etes the Slakll'lg 0f UHPPlVel'lZed'dO that an outstanding yincrease in surface area and decrease lime Yvllh lower Speelflc gfaVlflf aqueous Calelum Chloflde in MG(OH)2 particle size Was obtained in accordance Conlelllng @f me Slaklng SOIUUOHS elle a 10W Percentage 30 with the present improvement when surprisingly as little 0f he fequlele MgCl2 1U the .Slekef 111 eccoldace With as 2 percent of the requisite MgCl2 brine was added to the present invention. The slaking vessel iri this case conthe Blake; sisted of a ctntinuoilisly operated, horizontally disposed, In a manner similar to the foregoing, high density, gahugtln ntcl Slakefuwltltafskor hf blaesdt' high surface area Mg(OH)2 product is produced by the e e m e na wa s o .e s a er (as escn e m improved process by which a portion of the total Weight U.S. Paent 3,080,215). The dolime, Water, recycled pref b 0rd. a .l dded t th Ctio s 1 f m cipitator slurry, and 5.1 percent of the requisite MgCl2 o une m lya 0 9h area n Ye e l'e' ro brine were continually fed to the slaker. Substantially all about 1'5 to a out 8 we lg t pfnznt) 1s rst ad edf() the slaking took place at about a specic gravity of about the already Slaked d'ohme m a mlxlng Vessel- The rfimalm 1 109 Accordingly Suicient Water was added to the 40 der of the process is carried out in accordance with the slaker along with the precipitator slurry as slakng solu- PTOCeSS described in US Patent 3,080,215- Tlle resulttion to essentially provide the dolime slurry ltrate speciing Mg(0H)2 Pl'OdUC iS Suitable fOl use in making high fic gravity indicated. density, low porosity periclase.

TABLE Example I Example II Example III Example IV Com- Working Runs Coin- Working Com Working Com Working Runs parative parative Run parative Run parative Run A Run B III Run C IV Run D I I V VI Dolomitic Lime Slaker Operation:

Lbs/hr. of dolime 18. 25 21.4 None 0 76 Inventory time (minutes) 6. 5 Sp. Gr. of dolime slurry ltrat 1. 225 Precipitator Operation:

Gal./lir. of brine (remainder) 46. 5 Percent of MgCl2 brine 110W into precipitator 100 Filtrate sp gr. 1. 24g

6 Inventory time (hours 3.8 Mg(OH)2 Product Analysis:

Average Mg(OH) 2 particle size (microns) 7. 2 Dry Mg(OH)2 surface area (m.2/gm.) 7. 9 Resulting Periclase: Density (gnL/cc.) 2.953

While the dolime analyses of the present Example III was essentially the same as in Example I, the MgCl2 brine contained about 9.4 percent MgCl2 by Weight. Comparative run C is provided for purposes of comparison with run IV of the example and was carried out in accordance with U.S. Patent No. 3,080,215.

which will provide a lter cake of high density and high purity by calcining dolomite to produce dolime, slaking the dolime at a temperature of between 40 and 90 C. for at least about 4 minutes with a slaking liquid comprising an aqueous CaClz solution substantially free of magnesium ions, the liquid portion thereof having a speciic gravity of at least 1.07, thereby the produce a slaked dolime slurry, and interrnxing the dolime slurry so produced with an aqueous brine solution containing at least about 2 percent by weight of MgCl2 for a mixing period of at least about 2 hours at a temperature of within the range of from about 40 C. and about 80 C., the amount of the dolime slurry being suiicient to provide more than one mole of Ca(OH)2 per mole of MgCl2 thereby to produce solid magnesium hydroxide suspended in a CaCl2- containing brine, and recovering the thus-produced magnesium hydroxide, the improvement comprising:

(a) slaking the dolime with a slaking liquid comprising an aqueous calcium chloride solution of a specific gravity in the slaker of from about 1.07 to about 1.3 having in combination therewith from about 1.5 to about 80 weight percent of the requisite MgCl2-containing aqueous brine solution while maintaining a temperature in the brine, dolime and CaCl2 solution within the range of from about 40 to about 90 C. and continuing the slaking process for a period within the range of from about 4 minutes to about 3 hours, the amount of aqueous brine being d-irectly related to specific gravity of the slaking liquid;

(b) maxing the remainder of said requisite MgCl2- containing aqueous brine solution with the resulting dolime slurry; and

(c) maintaining the resulting mixture for at least about 2 hours at a temperature within the range of from about 40 to about 80 C.

2. In a process for producing magnesium hydroxide which will provide a filter cake of high density and high purity by calcining dolomite to produce dolime, slaking the dolime at a temperature of between 40 and 90 C.

for at least about 4 minutes with a slaking liquid comprising an equeous CaCl2 solution substantially free of magnesium ions and the liquid portion thereof having a specific gravity in the slaker of from about 1.07 to about 1.30, thereby to produce a slaked dolime slurry, and

intermixiug the dolime slurry so produced with an aqueous brine solution containing at least about 2 percent by weight of MgCl2 for a mixing period of at least about 2 hours at a temperature of within the range of from about 40 and about 80 C., the amount of the dolime slurry being sufficient to provide more than one mole of Ca(OH)2 Iper mole of MgCl2 thereby to produce solid magnesium hydroxide suspended in a CaClZ-containing brine, and recovering the thus-produced magnesium hydroxide, the improvement comprising:

(a) introducing into the slaked dolime slurry from about 1.5 to about 80 weight percent of said requisite MgCl2-containing aqueous brine solution while maintaining a temperature within the range of from 40 to about 90 C. for a period within the range of from about 4 minutes to about 3 hours; l

(b) adding to the resulting reaction mixture of said MgCl2-containing brine and dolime slurry, the remainder of said requisite MgCl2-containing aqueous brine solution; and

(c) maintaining this mixture at least for about 2 hours at a temperature within the range of from about 40 to about 80 C.

References Cited UNITED STATES PATENTS 2,893,840 7/1959y Vettel et al 23-201 3,080,215 3/1963 Waldron et al 23-201 3,294,485 12/1966 Mayer 23-201 X MILTON WEISSMAN, Primary Examiner.

OSCAR R. VERTIZ, Examiner.

G. T. OZAKI, Assistant Examiner. 

